Download Data Warehouse

Ch3 Data Warehouse
Modified from a presentation
by Dr. Bernard Chen Ph.D.
University of Central Arkansas
Fall 2009
What is Data Warehouse?

Loosely speaking, a data warehouse refers to a
database that is maintained separately from an
organization’s operational database

Officially speaking:

“A data warehouse is a subject-oriented, integrated,
time-variant, and nonvolatile collection of data in
support of management’s decision-making
process.”—W. H. Inmon
Data Warehouse—SubjectOriented

Organized around major subjects, such as customer,
product, sales

Focusing on the modeling and analysis of data for
decision makers, not on daily operations or
transaction processing

Provide a simple and concise view around particular
subject issues by excluding data that are not useful
in the decision support process
Data Warehouse—Integrated


Constructed by integrating multiple, heterogeneous data
sources
 relational databases, flat files, on-line transaction records
Data cleaning and data integration techniques are applied.
 Ensure consistency in naming conventions, encoding
structures, attribute measures, etc. among different data
sources
 E.g., Hotel price: currency, tax, breakfast covered, etc.
 When data is moved to the warehouse, it is converted.
Data Warehouse—Time
Variant

The time horizon for the data warehouse is
significantly longer than that of operational
systems


Operational database: current value data
Data warehouse data: provide information from a
historical perspective (e.g., past 5-10 years)
Data Warehouse—Nonvolatile

A physically separate store of data transformed from the operational
environment

Operational update of data does not occur in the data warehouse
environment

Does not require transaction processing, recovery, and concurrency
control mechanisms

Requires only two operations in data accessing:

initial loading of data and access of data
Data Warehouse vs.
Heterogeneous DBMS

Traditional heterogeneous DB integration: A query driven
approach


Build wrappers/mediators on top of heterogeneous databases
Data warehouse: update-driven, high performance

Information from heterogeneous sources is integrated in advance
and stored in warehouses for direct query and analysis
Data Warehouse vs.
Operational DBMS

OLTP (on-line transaction (query) processing)



Major task of traditional relational DBMS
Day-to-day operations: purchasing, inventory, banking,
manufacturing, payroll, registration, accounting, etc.
OLAP (on-line analytical processing)

Major task of data warehouse system

Data analysis and decision making
Data Warehouse vs.
Operational DBMS

Distinct features (OLTP vs. OLAP):

User and system orientation: customer vs. market

Data contents: current, detailed vs. historical, consolidated

Database design: ER + application vs. star + subject

View: current, local vs. evolutionary, integrated

Access patterns: update vs. read-only but complex queries
Data Warehouse vs.
Operational DBMS
OLTP
OLAP
users
clerk, IT professional
knowledge worker
function
day to day operations
decision support
DB design
application-oriented
subject-oriented
data
current, up-to-date
detailed, flat relational
isolated
repetitive
historical,
summarized, multidimensional
integrated, consolidated
ad-hoc
lots of scans
unit of work
read/write
index/hash on prim. key
short, simple transaction
# records accessed
tens
millions
#users
thousands
hundreds
DB size
100MB-GB
100GB-TB
metric
transaction throughput
query throughput, response
usage
access
complex query
Why Separate Data
Warehouse?

High performance for both systems


DBMS— tuned for OLTP: access methods,
indexing, concurrency control, recovery
Warehouse—tuned for OLAP: complex
OLAP queries, multidimensional view,
consolidation